1. Field of the Invention
The invention pertains to a drive sprocket wheel for a track-type undercarriage with several tread rollers and an endless chain, especially for cranes.
2. Description of the Related Art
A drive sprocket wheel of the general type in question is known from GB 1,602,143. This consists of a toothed wheel, provided with teeth around its circumference, and two treads, one on each side of the toothed wheel. As a result of the difference between the larger diameter of the root circle of the toothed wheel and the smaller outer diameter of the treads, a wheel flange is formed on each side; these flanges cooperate with the links of the endless chain. The endless chain consists of multiple links, each with a base plate; each link also has two guide webs, which are symmetric to the center and spaced a certain distance apart, extending in the travel direction. The webs have engaging surfaces which ride on opposed circumferential flanges of the sprocket wheel. A cog connects the two webs below the engaging surfaces and meshes with the teeth of the drive sprocket wheel. The pitch angle, obtained by dividing 360 degrees by the number of teeth, is constant around the entire circumference. The disadvantage of the known solution is that, when a crane is traveling downhill, it must be braked. Because the clearance is the same in all spaces between teeth of the toothed wheel, a shift in the relationship between the drive sprocket wheel and the endless chain thus occurs, with the result that the head area of the tooth affected by this shift runs up against the flank of the cog. In the least favorable case, the tooth shears off the flank of the cog, which leads to a further deterioration in the meshing conditions, which can become noticeable as loud noise. The problems just described can also occur when a change is made from forward to reverse travel.
The task of the invention is to improve a drive sprocket wheel of the general type in question so that the disadvantages described above are avoided.
In accordance with the principle of the invention, each tread has a stationary mounting ring connected to the toothed wheel, and a rotating ring is supported in bearings on the stationary mounting ring with the freedom to rotate. The bearings can be designed as plain bearings or as roller bearings. It is advantageous to install guide rings. For example, a guide ring of the type in question is offered by Busak+Shamban under the trade name xe2x80x9cLuytexxe2x80x9d. The material is a composite textile material of finely woven synthetic fabric with added lubricants and is impregnated with special hot-setting polyester resins. The guide rings are cut at a slant and have the required gap dimension Z. To protect against dirt, seals are provided, one on the inside and one on the outside of the rotating rings. The stationary mounting ring preferably has on the outside a stop collar, against which the rotating ring can be supported axially. In this arrangement, it is necessary for the treads to be connected detachably to the toothed wheel, so that it is possible to install the rotating ring on the stationary mounting ring. As an alternative, it is also possible to connect the stop collar detachably to the stationary mounting ring, so that the stationary mounting ring can be an integral part of the toothed wheel.
The advantage of the design of the drive sprocket wheel proposed here is that the toothed wheel can rotate relative to the rotating rings, including the base plates. This means that the base plate is always oriented correctly to the drive sprocket wheel, and thus the danger that a tooth of the drive sprocket wheel will run up against the chain is reduced. Operating tests have shown that track-type undercarriages equipped in this manner operate more smoothly than track-type undercarriages according to the state of the art.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.